A. FIELD OF THE INVENTION
The present invention relates to insulation material, and more particularly to an insulation material including a substantially homogeneous mixture of inorganic non-flammable fibrous material and discrete expanded silicate particles substantially homogeneously dispersed throughout the fibrous material.
B. DESCRIPTION OF THE PRIOR ART
Inorganic fibrous materials have long been used in the field of insulation. Typically, the inorganic fibrous materials include rock or mineral wools, which are formed by blowing a jet of steam through molten rock or slag, or glass wools. The insulation efficiency of the material, which is known as the R value of the material, is attributable not to the material itself, but to the air trapped among the fibres. In the extreme case, if the fibrous material were compacted such that there were no intersticial air, then the R value would be exceedingly low. At the other extreme, if the fibrous material were so loose as not to trap air, then convection currents of air could flow easily through the material, again making quite small the R value. Thus, there is a theoretical optimum density of the fibrous material.
When the fibrous material is applied, either in blown form or in mats, the optimum density is substantially achieved. However, with time, the fibrous material settles and compacts. The settlement occurs because of the weight of the material and is accelerated by vibrations, which are ever present. As the fibrous material settles, it traps less air and its R value decreases. In some cases, after a few years, the settlement may be so great as to reduce by as much as fifty percent the R value of the insulation.
In addition to using inorganic fibrous material as a loose fill or mat material, such fibrous material is used in wet spray applications. In wet spray, the fibrous material is mixed with a liquid adhesive and sprayed onto a wall or ceiling where it dries and forms an insulating layer. Again, the primary insulating effect is due to air trapped between and among the fibres within the adhesive. However, the force of the spray in applying the mixture of fibrous material and adhesive forces out substantially all of the air and, accordingly, the R value of wet sprayed inorganic fibre is less than optimum.
Alternative products to inorganic fibrous material have been developed. One such class of alternatives is expanded amorphous glass particles, including sodium silicate, perlite, zonalite, and vermiculite. One product that has been found to be useful is that formed by the process of U.S. Pat. No. 4,203,773. All such products are lightweight particles having substantial air entrapped therein. The particles are used primarily by covering a ceiling with a layer thereof. The expanded glass insulation materials have an R value substantially higher than that of inorganic fibrous materials and, due to their rigidity, have substantially no settlement with time. However, for equal R values, the area coverage of expanded particulate insulation materials is substantially less than that of inorganic fibrous insulation materials. Accordingly, while expanded particulate materials are more efficient insulators, their cost is substantially higher than inorganic fibrous materials.
Because the air is trapped within the expanded glass particles and not between and among the fibres of inorganic fibrous insulation materials, expanded glass particles would appear to be useful in wet spray applications. The adhesive would bond together the particles, but there would be no reduction in the amount of trapped air within the adhesive-particle mixture. However, wet spray applications of expanded particulate materials have not been entirely satisfactory. A substantial number of particles upon impact with the surface to be covered bounce, rather than stick. Thus, in wet spray applications of expanded particulate material, there is substantial waste.
It is therefore an object of the present invention to provide an improved insulation material that overcomes the shortcomings of the prior art. More specifically, it is an object of the present invention to provide an economical insulation material that has a high R value, good coverage, and substantially no tendency to settle. It is a further object of the present invention to provide an insulation material that is suitable for wet spray applications that provides good insulation value without waste.